Synthesis and Characterization of Refractory Oxides Doped with Transition Metal Ions

Abstract

In this study, the oxygen-deficient TiO2, SrTiO3 systems and transition metal ion (Cr or V) doped TiO2, SrTiO3 and SrZrO3 systems have been investigated. We prepare samples as polycrystals, single crystals and thin films for various desires. Their structural, physical and electronic properties are measured by bulk-sensitive techniques (X-Ray Diffraction, SQUID and Electro Paramagnetic Resonance) or surface-sensitive techniques (Photoemission spectroscopy and X-ray absorption spectroscopy). The measurement of SQUID and EPR shows not only their magnetic properties but also the valence state of Cr dopant. We verify the valence state of Cr ions in Cr:TiO2, Cr:SrTiO3 and Cr:SrZrO3 with three forms of samples, polycrystals, single crystals or films. We try to find the key parameters of sample synthesis which control the valence state of Cr ions. The cluster containing various valence states of Cr or the segregated phases such as CrO3 or SrCrO4 can be formed when the sample was synthesized under O2 rich environment. Cr ions in those systems tend to be oxidized easily under O2 rich environment. The surface properties of Cr-doped SrZrO3 films are also discussed. We find the synthesis conditions which influence on not only the behavior of Cr ions but also the resistive-switching behaviors. The surface chemistry of Cr:SrZrO3 films is studied using Photoemission spectroscopy (PES) and X-ray absorption spectroscopy (XAS). We observed that an interface state of Pt and Cr:SrZrO3 which exhibited the reversible RS behavior. This kind of the interface state can derive from the surface reconstruction when the external electric-field induces large thermal energy. This interface state can act as an oxygen reservoir for the reversible migration of oxygen ions and vacancies which would be needed for RS behavior.